From 9456f0fa6d3cb944d3b9fc31c9a244e0362c26ea Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 6 May 2009 21:54:09 -0400 Subject: tracing: reset ring buffer when removing modules with events Li Zefan found that there's a race using the event ids of events and modules. When a module is loaded, an event id is incremented. We only have 16 bits for event ids (65536) and there is a possible (but highly unlikely) race that we could load and unload a module that registers events so many times that the event id counter overflows. When it overflows, it then restarts and goes looking for available ids. An id is available if it was added by a module and released. The race is if you have one module add an id, and then is removed. Another module loaded can use that same event id. But if the old module still had events in the ring buffer, the new module's call back would get bogus data. At best (and most likely) the output would just be garbage. But if the module for some reason used pointers (not recommended) then this could potentially crash. The safest thing to do is just reset the ring buffer if a module that registered events is removed. [ Impact: prevent unpredictable results of event id overflows ] Reported-by: Li Zefan LKML-Reference: <49FEAFD0.30106@cn.fujitsu.com> Signed-off-by: Steven Rostedt --- kernel/trace/trace.c | 10 ++++++++++ kernel/trace/trace.h | 2 ++ kernel/trace/trace_events.c | 9 +++++++++ 3 files changed, 21 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 4164a344e72..dd40d232034 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -639,6 +639,16 @@ void tracing_reset_online_cpus(struct trace_array *tr) tracing_reset(tr, cpu); } +void tracing_reset_current(int cpu) +{ + tracing_reset(&global_trace, cpu); +} + +void tracing_reset_current_online_cpus(void) +{ + tracing_reset_online_cpus(&global_trace); +} + #define SAVED_CMDLINES 128 #define NO_CMDLINE_MAP UINT_MAX static unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1]; diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 777c6c3a0cd..ba25793ffe6 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -409,6 +409,8 @@ int tracing_is_enabled(void); void trace_wake_up(void); void tracing_reset(struct trace_array *tr, int cpu); void tracing_reset_online_cpus(struct trace_array *tr); +void tracing_reset_current(int cpu); +void tracing_reset_current_online_cpus(void); int tracing_open_generic(struct inode *inode, struct file *filp); struct dentry *trace_create_file(const char *name, mode_t mode, diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 8d579ff2361..6d2c842a024 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -932,9 +932,11 @@ static void trace_module_remove_events(struct module *mod) { struct ftrace_module_file_ops *file_ops; struct ftrace_event_call *call, *p; + bool found = false; list_for_each_entry_safe(call, p, &ftrace_events, list) { if (call->mod == mod) { + found = true; if (call->enabled) { call->enabled = 0; call->unregfunc(); @@ -957,6 +959,13 @@ static void trace_module_remove_events(struct module *mod) list_del(&file_ops->list); kfree(file_ops); } + + /* + * It is safest to reset the ring buffer if the module being unloaded + * registered any events. + */ + if (found) + tracing_reset_current_online_cpus(); } static int trace_module_notify(struct notifier_block *self, -- cgit v1.2.3